As with all mechanical devices, fuel injectors have physical dimensions that lead to variations between fuel injectors. In addition, each fuel injector has different rates of wear and responds to temperature changes differently. Since the fuel delivered by each fuel injector during a fuel injection event varies enough to affect the performance of an associated engine, it is useful to measure or calculate the fuel delivery by each fuel injector. Current systems stop fuel flow to a fuel accumulator for a specific time, leading to performance and emission challenges when the fuel pressure in the accumulator falls to a level that affects fuel injection.